1. Field of the Invention
The present invention relates to a primer for adhesive sheets, an article attached with an adhesive sheet and a process for producing the article. More particularly, the present invention relates to a primer for adhesive sheets which can prevent cleavage, peeling and displacement of the adhesive sheet, maintain excellent properties and be handled easily even when the adhesive sheet is attached to an adherend in a short time after the primer is applied to the adherend; an article attached with an adhesive sheet which is obtained by attaching the adhesive sheet to an adherend using the primer as the intermediate layer; and a process for producing the article attached with an adhesive sheet effectively.
2. Description of Related Art
Recently, adhesive sheets (including adhesive tapes; similarly, hereinafter) have been used widely in many fields. For example, adhesive sheets are used for packages and bindings, office and household uses, bonds, masks in coating, surface protection, sealing, corrosion prevention, shielding from water, electric insulation, electronic instruments, medical and hygienic materials, displays, marks, decorations and labels.
In the fields of displays, marks and decorations among the above applications of the adhesive sheets, the demand for adhesive sheets as the replacement for coating films, i.e., films formed in accordance with the coating process, has been increasing to achieve an improvement in productivity and a decrease in production cost of coated articles. For example, tapes for warning danger, line tapes and marking tapes are used for displaying and marking. In the field of decoration, adhesive sheets are used for interior and exterior decorations of show windows and buildings, decoration of automobiles and motor cycles with marking sheets and stickers and decoration of door sash portions of automobiles. Adhesive sheets having a substrate having the retroreflection property which reflects light to the direction of the incident light are used for marks for roads, railroads and related facilities as reflection sheets.
As the adherend to which an adhesive sheet is attached as the replacement for a coating film, various materials are used. For example, metal plates, coated metal plates, glass, ceramics, stone materials, wood materials, plastics and paper are used.
Since articles attached with an adhesive sheet as the replacement for a coating film are frequently used outdoors, it is necessary that both of the substrate and the adhesive have excellent weatherability and, in general, acrylic adhesives having excellent weatherability are used as the adhesive. It is preferable that the substrate has excellent weatherability and a small shrinkage and it is also preferable that rigidity is not excessively great from the standpoint of workability. Therefore, film substrates comprising, for example, polyvinyl chloride, polyesters, polypropylene, polyacrylates, polycarbonates, polytetrafluoroethylene and thermoplastic polyurethanes are used. From the standpoint of economy, film substrates comprising polyvinyl chloride are frequently used at present.
It is required that the article attached with the adhesive sheet as the replacement for a coating film do not show cleavage, peeling or displacement of the adhesive sheet for a long time.
It is considered that cleavage, peeling and displacement of the adhesive sheet with passage of time are caused, for example, by (1) separation at the interface of the substrate and the adhesive layer, (2) a decrease in the ability of the adhesive itself to hold the sheet and (3) separation at the interface of the adhesive layer and the adherend. The problem caused by (1) can be overcome, for example, by treating the substrate by corona discharge. The problem caused by (2) can be overcome by using an adhesive having a greater holding ability. To overcome the problem caused by (3), the adherend may be coated with a primer and the adhesive sheet may be attached to the primer. However, it is the actual situation at present that no satisfactory primer for adhesive sheets can be found.
The properties required for the primer used for attaching an adhesive sheet as the replacement for a coating film to an adherend are as follows: (1) cleavage, peeling and displacement of the adhesive sheet can be prevented even when the adhesive sheet is attached in a short time after the primer is applied to the adherend and the primer exhibit the excellent effect of maintaining the property; (2) the primer has an excellent coating property and, for example, can be applied by a felt pen; and (3) the primer is a one-part composition which spontaneously dries or is cured with moisture and does not require any specific apparatus such as a drier.